Variable depth streamer technology for enhanced seismic interpretation

Transcription

1 Variable depth streamer technology for enhanced seismic interpretation Gregor Duval*, Steven Bowman, Roger Taylor, Yves Lafet, Adrian Smith and Henning Hoeber

2 Content Introduction: why does the seismic interpreter need broadband data? Benefits for interpretation of a wide range of geological settings: Tertiary silici-clastic reservoirs Chalk section Deep sub-bcu targets

3 Why does the seismic interpreter need broadband data?

4 Effects and benefits of increasing the bandwidth 10-20Hz 10-25Hz 10-30Hz 10-35Hz Large side-lobes and broad central peak Sharper central peak Increasing high frequencies 10-20Hz Increase low frequencies 5-20Hz 2-20Hz Reduced side-lobes

5 Effects and benefits of increasing the bandwidth BroadSeis Conventional 20 m 1000 m Conventional Courtesy of Total, Cobalt and the Republic of Gabon BroadSeis

6 Effects and benefits of increasing the bandwidth Courtesy of Total, Cobalt and the Republic of Gabon

7 CPI log showing thin/complex formations 7

8 Seismic synthetic model Impedance Conventional seismic synthetic Conventional seismic data at well location Broadband seismic synthetic

9 Seismic synthetic model Impedance Conventional seismic synthetic Conventional seismic data at well location Broadband seismic synthetic Prominent side-lobe interfering with interpretation of conventional seismic data

10 Seismic synthetic model Impedance Conventional seismic synthetic Conventional seismic data at well location Broadband seismic synthetic Peaks and troughs fit better with well marker on broadband model

11 Seismic synthetic model Impedance Conventional seismic synthetic Conventional seismic data at well location Broadband seismic synthetic Obvious impedance gradient No impedance gradient Obvious impedance gradient NB: The low frequency component of broadband data give a better feel of the actual impedance gradients, which should in turn provide better seismic inversion results

12 Interpretation of Tertiary siliciclastic reservoirs

13 Conventional Interpretation of a gas reservoir Side lobes GR IP

14 Broadband Interpretation of a gas reservoir GR IP

15 Broadband Interpretation of a gas reservoir

16 Broadband Interpretation of a gas reservoir

17 Broadband Interpretation of a gas reservoir

18 Broadband Interpretation of a gas reservoir

19 Conventional Ip from AVO inversion

20 Broadband Ip from AVO inversion BroadSeis pre-stack inversion gives a more stable result: 1 The GWC flat spot is better resolved 2 Values of Ip within the gas column are more accurate and more homogeneous

21 Conventional Tay fan imaging (zoomed)

22 Broadband Tay fan imaging (zoomed)

23 Broadband filtered Tay fan imaging Bandpass filter applied: 10-40Hz 50-70Hz to approximately match spectrum of Conventional data

24 Conventional Tay fan imaging

25 Conventional Low frequency Tay fan imaging Bandpass filter applied: 0-4Hz 6-10Hz

26 Broadband Low frequency Tay fan imaging Bandpass filter applied: 0-4Hz 6-10Hz

27 Conventional Tertiary channel interpretation Mey channel

28 Broadband Tertiary channel interpretation Top Mey sandstone

29 Broadband Tertiary channel interpretation Top Mey sandstone

30 Conventional Section through polygonal faults and contourites

31 Broadband Section through polygonal faults and contourites

32 Conventional Shallow section interpretation Autopicking with waveform correlation tool on a wide window is noisy (spiky) on band limited data

33 Broadband Shallow section interpretation Autopicking works a lot better on Broadband data, less spiky

34 Interpretation of Chalk facies

35 Conventional Well tie and Chalk interpretation

36 Broadband Well tie and Chalk interpretation

37 Broadband Well tie and Chalk interpretation This low impedance, marly interval correlates with the edge of a bright amplitude dissolution feature in the upper chalk section on the seismic data.

38 Conventional Ekofisk/Maureen RMS amplitude map Upper Chalk clay ponds and dissolution features 1km

39 Broadband Ekofisk/Maureen RMS amplitude map Upper Chalk clay ponds and dissolution features 1km The chalk dissolution features (clay pools) are much better defined on broadband data The gray scale trends in the background highlight the regional facies variations: darker grays to the left are indicative of a marlier chalk section whereas light grays correspond to hard, carbonate-rich chalk.

40 A recent Chalk discovery: Orchid 40

41 Orchid as interpreted on conventional data 41 Source: Trap Oil investor presentation

42 W-E regional seismic line with interpretation Salt-induced high Orchid West Central shelf Zechstein salt 42

43 S-N regional seismic line with interpretation Orchid Salt-induced high Zechstein salt 43

44 W-E seismic line across Orchid Phase reversal due to soft response from the oil-filled chalk reservoir? Flat-spot or porosity effect (or both)? 44

45 NE-SE arbitrary seismic line across Orchid Large salt diapir towards the NW Central Orchid is offset by a large fault initiated due to uplift from the Zechstein salt below 45

46 Orchid chalk reservoir as interpreted on broadband data Broadband data do not show amplitude dim in the central part of the field TWT structure map Top Chalk amplitude map Minimum amplitude map directly below Top Chalk 46

47 Interpretation of deep sub-bcu targets

48 Fault blocks interpretation using band-limited data BCU????? Jurassic fault blocks Cross fault correlation with multiple choices?? Any reflector can be correlated through faults

49 Fault blocks interpretation using broadband data BCU Jurassic fault blocks Cross fault correlation better understood Uniqueness of the reflector correlation through faults

50 Conventional Jurassic fault blocks interpretation

51 Broadband Jurassic fault blocks interpretation

52 Broadband Jurassic fault blocks interpretation

53 Conventional Jurassic fault blocks interpretation

54 Conventional Well synthetic, deep tie NB: Well synthetic phase reversed for display purposes

55 Broadband Well synthetic, deep tie Low frequency package NB: Well synthetic phase reversed for display purposes This sub-bcu low frequency package is clearly visible on broadband seismic but not on conventional data, and it is replicated by a well seismic synthetic. This means that this is the genuine formation signature and that the low frequencies below the BCU are not coming from any kind of noise.

56 Summary Benefits for qualitative interpretation BroadSeis data provide a broader frequency spectrum enabling the interpreter to: Accurately interpret stratigraphy, thin beds and subtle structures benefit from the high frequencies Produce a clearer interpretation of deep targets (sub-bcu, sub-chalk, subbasalt ) and large-scale and subtle facies variations benefit from the low frequencies Extract the true seismic signature of the geological formations by reducing the wavelet side-lobes and sharpening its central peak benefit from the broad frequency range

57 Broadband shallow imaging 57

58 Acknowledgments CGG multi-client division for permission to show these data examples Steven Bowman, James Rigg and Steve Thompson - interpretation of seismic data and images contribution Vincent Durussel, Steve Hollingworth and their team - seismic processing

59 THANK YOU! 59